it must be in multiplayer and you must have cheats on (in console (activated by pressing shift + ~) type devmap <mapname>)
when in the game, have the lightsaber selected but not on and in console type /thedestroyer

Dude, don't bother messing with the Double Bladed Lightsaber. Lets start looking for two lightsabers! I wanna be just like Boc heh.

But really, the the Double Bladed Lightsaber isn't that cool... they didn't make it right... sticks through you, kills people behind you, doesn't cut through things. Sparks, but doesn't cut through things (or my settings were screwed up) Wait for some mods... now those guys can make the multiplayer part of the game better.